In some trees, it becomes important to assist in the support of weak limbs by using steel cables. Many times the reason for a cable is due to a possible target (i.e. the house or a high use area) .Often times the tree that is in need of a cable is old or has a structural defect such as a splitting limb or a tight trunk crotch union.  When a cable is to be installed, it is very important to understand some basic facts about how cables are effective. An improper or poor installation of a cable may just be a false sense of security. You also need to know that cables are not insurance that the limbs will never fail. Cables should not be used in cases where the decay or defect is severe. Cables should not be installed and forgotten. They need future inspection to determine wood weakness or in some cases extreme dependency. When a cable becomes the main support for a limb that can no longer hold itself, then you may be setting yourself up for a much greater failure.  Often, when a large tree gets so heavy, and a limb that has grown dependent on a cable snaps, then other parts of the tree that are also connected by cables, become stressed or fractured due the failure of one limb.  In other words, when a tree has a network of cables, it is the whole network that makes the cable system work.  Take out one part of the network and sometimes another part of the tree becomes too heavy for the cables that were connected to the balance of the rest of the tree.

When the decision to install cables becomes important, the location of the cables and the stresses placed on other parts of the tree need to be considered.If a limb can be made safe by trimming (end-weight reduction), without compromising the health of the limb, then that is generally a better approach.

Very important!
The angle of the cables, the distance up in the canopy, the line up of the bolts, the centering of the holes in the limbs, and the type of cables and attachments used are all factors that need consideration. All too often, a poor cable installation is a wasted effort and in some cases, increases the possibility of a tree failure.

Be sure you are confident of the ability of the person who intends to do the installation. Ask about the person's training in cable installation. If the company you hire sends out an inexperienced person to do a cable job, then your tree may be worse off than before.

There are many different types of systems and techniques for cabling.  Ask the Arborist just how it will be done before work commences.The better informed you are about what is being done, the better your chances are of getting a quality job.

Braces
Are another aspect of tree support that needs addressing. Outside supports of either wood or steel are sometimes needed to hold up a tree (or limb) that will not support itself. I have built A-frames to hold up trees that were starting to topple. A poor root structure, or damaged roots, can lead to an imbalance and possibly the need for a prop. Orchard owners know about the need to prop heavy, fruit laden, limbs as a temporary assist.